The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Circuits may be classified as type A and B. The classification of the circuit is based in part on a portion of the input signal cycle during which the circuit conducts.
In Class A type circuits, 100% of the input signal is used. Where efficiency is not a consideration, most small signal linear amplifiers are designed as Class A type circuits. While Class A type circuits are typically more linear and less complex than other circuit types, they are relatively inefficient.
Class B type circuits use 50% of the input signal. In most Class B type circuits, there are two output devices that conduct alternately during half cycles. Some distortion may occur in Class B type circuits. While distortion is usually worse at higher frequencies, distortion may also occur at lower frequencies due to kickback.
Referring now to FIG. 1, an exemplary Class B type circuit 10 is shown. The circuit 10 includes controllable current sources 12, 14, 16 and 18. During one half cycle, the current sources 12 and 18 supply current in a first direction across a load 20. During a second half cycle, the current sources 14 and 16 provide current across the load 20 in an opposite direction.
Class B type circuits such as current digital to analog converters (DACs) do not work in differential arrangements. As a result, a large kick-back is usually seen at a control terminal of current sources in Class B type circuits if there is not enough voltage headroom to use cascode devices, which can cause distortion.